‘if men were not employed to prune these trees… they would cover the country, completely invading it.’

Sound familiar? It could be a description of any number of invasive trees, from the trumpet tree (Cecropia peltata) spreading through West Africa to the candlenut tree (Aleurites moluccanus) currently invading Pacific islands. But it’s actually an account by Mas’ūdī, writing over a thousand years ago in the Islamic year 332 (943 CE).

Born in Baghdad around 890 CE, Mas’ūdī was a prolific writer and adventurer extraordinaire. His world-history-meets-travelogue, The Meadows of Gold, contains many fantastic stories, from jewelled tombs to Viking battles, but it was his account of an apparent invasive – referred to simply as the banyan tree – that caught my attention, and I was keen to find out more.

Mas’ūdī doesn’t give us much to go on: banyan is a broad term for an epiphytic fig – that is, a fig that begins life growing on another plant – and can be applied to a number of species; and the location is given as Saymūr, in the kingdom of Balharā, which roughly corresponds to the modern Indian state of Maharashtra.

So, opening CABI’s Invasive Species Compendium (ISC), I searched for ‘Banyan AND India’ and used the Filter by Type function to search for only full datasheets. This gave me nine results.

Sadly, Mas’ūdī provides no further distinguishing remarks, and with no more information to go on, the trail quickly ran cold. Was one of these Ficus species Mas’ūdī’s invasive banyan, already causing trouble over a thousand years ago?

It’s an enticing thought, but there are some caveats to acknowledge. Writing as he was many centuries before the advent of biology, we mustn’t take Mas’ūdī too literally – he does, after all, solemnly declare the rhino incapable of bending its legs. Equally importantly, we need to be careful not to confuse natural range expansion with human-mediated introductions. The natural world is constantly in flux and species’ ranges are never static, but expand and contract in response to a variety of environmental factors.

So, an intriguing but inconclusive investigation. Plus I managed to sneak in a brief demo of searching the ISC.